Effects of spot size on the temperature response of an aluminum alloy irradiated by a continuous laser
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摘要: 为了探究不同光斑尺寸连续激光辐照6061铝合金的温度响应及热致损伤问题，基于ANSYS有限元软件建立了激光辐照下的三维物理模型；使用不同的激光参数进行激光辐照实验，根据所采集的温度和前表面散射光强度数据，反演计算了靶材在激光辐照过程中吸收率的动态变化；最后，利用优化后的模型分析了不同光斑尺寸下，激光辐照靶材的温升特点。研究结果表明：在1000 W/cm2的激光辐照条件下，材料的吸收率随着温度的升高而升高；由于激光加载的局域化特征，横向热扩散影响纵向温升，光斑足够大时该影响变小，这与其热扩散长度有关；对于4 mm厚的6061铝合金材料，当光斑尺寸大于10 cm时，光斑影响可以忽略，靶材背表面发生熔融损伤时间阈值保持2.6 s不变。Abstract: In order to investigate the temperature response and thermal damage of a 6061 aluminum alloy after variations in spot size of continuous laser irradiation, a three-dimensional physical model under laser irradiation was established based on ANSYS finite element software. First, we used different laser parameters to carry out laser irradiation experiments, and then, based on the collected temperature and front surface scattered light intensity data, we calculated the dynamic changes in the absorptivity of the target during laser irradiation. Finally, the optimized model was used to analyze the temperature rise characteristics of the target irradiated by lasers at different spot sizes. The research results show that the absorption rate of the material increases with an increase in temperature under 1000 W/cm2 laser irradiation. Due to the localized characteristics of laser loading, lateral thermal diffusion affects the longitudinal temperature rise, and its effect becomes smaller when the spot is larger, as related with the alloy’s thermal diffusion length. For the 6061 aluminum alloy material with a thickness of 4 mm, when the spot size is greater than 10 cm, the effect of the spot’s size is negligible, and the time threshold of fusion damage on the back surface of the target remains unchanged at 2.6 s.
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Key words:
- Laser irradiation /
- Numerical simulation /
- Temperature field /
- Spot size
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图 2 材料的密度（a）、热导率（b）、热焓（c）随温度的变化情况
Figure 2. Change of thermal properties of the material with temperature. (a) Density; (b) thermal conductivity; (c) enthapy
图 4 在1000 W/cm2激光辐照条件下铝合金背面中心位置的温升曲线
Figure 4. Temperature rise curves at the center of aluminum alloy back under 1000 W/cm2 laser irradiation
图 6 激光辐照下铝合金前-背表面中心位置的温升曲线。（a）1000 W/cm2；（b）1500 W/cm2；（c）2000 W/cm2
Figure 6. Front-rear surface temperature as a function of time in the central area under laser irradiation. (a) 1 000 W/cm2; (b) 1 500 W/cm2; (c) 2 000 W/cm2
图 7 不同光斑尺寸的激光辐照下铝合金前-背表面中心的温升曲线
Figure 7. Front-rear surface temperature as a function of time in the central area under laser irradiation with different spot sizes
图 8 不同尺寸光斑激光辐照下铝合金前表面温度分布。（a）5 cm×5 cm；（b）10 cm×10 cm；（c）30 cm×30 cm；（d）50 cm×50 cm；（e）温度随R的变化图；（f）温度梯度随R的变化图
Figure 8. Temperature distribution in the front surface of aluminum alloy under laser irradiation with different spot sizes. (a) 5 cm×5 cm; (b) 10 cm×10 cm; (c) 30 cm×30 cm; (d) 50 cm×50 cm; (e) graph of temperature vs
$R$ ; (f) graph of temperature gradient vs$R$ 
图 9 光斑尺寸为30 cm×30 cm的激光辐照2 s时前表面温度场
Figure 9. Temperature field at the front surface when the laser spot size is 30 cm×30 cm and irradiating time is 2 s
表 1 6061铝合金成分[19]
Table 1. Composition of 6061 aluminum alloy
（%） $w({\rm{Mg}})$ $w({\rm{Si}})$ $w({\rm{Mn}})$ $w({\rm{Fe}})$ $w({\rm{Cr}})$ $w({\rm{Cu}})$ $w({\rm{Zn}})$ $w({\rm{Al}})$ 1.06 0.53 0.43 0.38 0.17 0.33 0.16 余量 
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表 2 不同温度下6061铝合金表面换热系数[22]
Table 2. Surface heat transfer coefficients of 6061 aluminum alloy at different temperatures
$T$/（℃） 20 100 200 300 400 500 600 700 $h$/（ W/m2·℃） 8.22 11.0 13.7 23.2 33.4 46.8 58.0 68.5
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表 3 6061铝合金激光吸收率参数设置
Table 3. Parameter settings of laser absorptivity of 6061 aluminum alloy
Temperature
range/ (℃)0~200 200~380 380~450 450~525 525~800 α 0.19 0.25 0.27 0.32 0.74
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